Allograft inflammatory factor (AIF-1) or ionized calcium-binding adapter molecule 1 (Iba1) is a cytosolic actin binding protein containing a calcium binding domain (EF-hand) and inducible by cytokines and INF-gamma (1). AIF-1 (theoretical molecular weight 17kDa) was first cloned from rat and human cardiac allografts and macrophage cell lines. In cardiac allografts, expression of AIF-1 was specifically associated with infiltrated mononuclear cells (2, 3). AIF-1 is constitutively expressed and inducible in macrophages and microglia. Iba1, microglia response factor (MRF-1) and daintain were independently cloned and identified in rat and human tissues and share complete sequence identity with AIF-1. Additionally, several AIF-1 splice variants have been identified including IRT-1, BART-1, G1 and Hara-1 (2).
Several cellular functions have been associated with AIF-1/Iba1 expression including cell growth, cell migration, actin bundling, membrane ruffling, and phagocytic activity (2, 4). Iba1 induces Rac signaling through a PLC-gamma dependent pathway (1). Rac, a member of the Rho family of small GTPases, localizes with Iba1 and F-actin in membrane ruffles and phagocytic cups and plays a role in microglia activation. AIF-1/Iba1 induction in macrophages and microglia occur in association with immunological inflammatory processes in various disease states including endometriosis, cerebral infarction and rheumatoid arthritis (5). Immunodetection of Iba1 through flow cytometry, immunohistochemical or immunocytochemical applications is commonly used for identification and analysis of microglia.
1. Imai, Y., & Kohsaka, S. (2002). Intracellular signaling in M-CSF-induced microglia activation: Role of Iba1. GLIA. https://doi.org/10.1002/glia.10149
2. Deininger, M. H., Meyermann, R., & Schluesener, H. J. (2002). The allograft inflammatory factor-1 family of proteins. FEBS Letters. https://doi.org/10.1016/S0014-5793(02)02430-4
3. Utans, U., Quist, W. C., Mcmanus, B. M., Wilson, J. E., Arceci, R. J., Wallace, A. F., & Russell, M. E. (1996). Allograft inflammatory factor-1: A cytokine-responsive macrophage molecule expressed in transplanted human hearts. Transplantation. https://doi.org/10.1097/00007890-199605150-00018
4. Franco-Bocanegra, McAuley, Nicoll, & Boche. (2019). Molecular Mechanisms of Microglial Motility: Changes in Ageing and Alzheimer's Disease. Cells. https://doi.org/10.3390/cells8060639
5. Kimura, M., Kawahito, Y., Obayashi, H., Ohta, M., Hara, H., Adachi, T.,... Yoshikawa, T. (2007). A Critical Role for Allograft Inflammatory Factor-1 in the Pathogenesis of Rheumatoid Arthritis. The Journal of Immunology. https://doi.org/10.4049/jimmunol.178.5.3316